Ricerc@Sapienza

Plasticity and damage are two fundamental phenomena in nonlinear solid mechanics associated with the development of inelastic deformations and the reduction of the material stiffness. Alessi et al. [5] have recently shown, through a variational framework, that coupling a gradient-damage model with plasticity can lead to macroscopic behaviours assimilable to ductile and cohesive fracture. Here, we further expand this approach considering specific constitutive functions frequently used in phase-field models of brittle fracture.

We propose a new variational fatigue phase-field model. The basic idea of the model is to let the fracture energy decrease as a suitably defined accumulated strain measure increases, which is obtained by introducing a dissipation potential which explicitly depends on the strain history. This amounts to a phenomenological description of a multitude of microscopic material degradation mechanisms, that are responsible for the macroscopic evidence of fatigue effects.

A novel multiscale strategy is proposed for the damage analysis of masonry structures modeled as periodic composites. Such a computational strategy, whose aim is to reduce the typically high computational cost exhibited by fully microscopic numerical analyses, is based on a multiscale/multidomain model equipped with an adaptive capability, which allows to automatically zoom-in the zones incipiently affected by damage onset.

The dynamical behavior of a mono-dimensional bar with distributed microcracks is addressed in terms of free and forced wave propagation. The multiscale model, derived from a generalized continuum formulation, accounts for the microstructure by means of a microdisplacement variable, added to the standard macrodisplacement, and of internal parameters representing density and length of microcracks. The influence of coupling between micro- and macrodisplacement overall response on the system is discussed, as well as the effect of the damage parameters on the propagating waves.

Between August 2016 and January 2017 nine shallow events with moment magnitude between 5.0 and 6.5 occurred in Central Italy, with largest magnitude being the most severe in Italy since 1980. Several thousands of heritage buildings have been affected to a different degree by the ground motion shaking, highlighting some specific behaviours in the most stricken areas. In and around Amatrice extensive masonry fragmentation, cracking of large walls without openings, as well as survival of tall towers and slender bell gables have been observed.

We operate a perturbation approach on the finite field equations for clamped slender arches with compact symmetric cross-section and parabolic centre curve under a uniform line load parallel to their symmetry axis. We study small vibration superposed on the relevant stress, assumed of membrane nature. We find the fundamental angular frequency in terms of the aspect ratio of the arch and of the pre-load; the possibility of buckling is examined. This is a first step towards monitoring such structures, and evaluating pre-loads and structural integrity by dynamic measurements.

Size-dependent structural behavior of inflected Timoshenko elastic nano-beams is investigated by nonlocal continuum mechanics. An innovative stress-driven integral model of elasticity is conceived by swapping source and output fields of Eringen's strain-driven theory. Unlike Eringen's model, the stress-driven nonlocal integral formulation leads to well-posed structural problems. Solution uniqueness and continuous dependence on data are thus ensured.

A nonlinearly coupled mathematical model of an electro-magneto-mechanical system is studied via the multiple scale approach in order to investigate its weakly nonlinear dynamics and analytically predict its salient features. The obtained amplitude modulation equations up to the third order perturbation allow to analytically describe the mechanical and electrical responses in terms of frequency-response curves and stability scenarios. A critical threshold of Hopf bifurcation is detected and analyzed as a function of the main system parameters.

The dynamics of a nonlinearly coupled electro-magneto-mechanical system is numerically investigated with the aim to obtain a comprehensive description of its behavior in strongly nonlinear regime. Bifurcation diagrams and stability charts as a function of the main system parameters allow to detect several multistable and unstable regions, characterized by coexistence of low-amplitude and high-amplitude responses, and by the presence of wide ranges of chaotic motions, which have been connoted by computing the relevant Lyapunov characteristic exponents.

This paper focuses on the development of energy dissipaters for rocking precast systems. The energy dissipaters developed in this work are to be used externally, having the advantages of being easy to inspect and replace after an earthquake. The main parameters to take into account for the development of the energy dissipaters are the cyclic behavior, the strength, and the ductility. The cyclic behavior has to be stable from cycle to cycle. The developed dissipater has to respond with adequate strength.